subtract_usage#

langchain_core.messages.ai.subtract_usage( left: UsageMetadata | None, right: UsageMetadata | None, ) → UsageMetadata[source]#

Recursively subtract two UsageMetadata objects.

Token counts cannot be negative so the actual operation is max(left - right, 0).

Example

from langchain_core.messages.ai import subtract_usage

left = UsageMetadata(
    input_tokens=5,
    output_tokens=10,
    total_tokens=15,
    input_token_details=InputTokenDetails(cache_read=4),
)
right = UsageMetadata(
    input_tokens=3,
    output_tokens=8,
    total_tokens=11,
    output_token_details=OutputTokenDetails(reasoning=4),
)

subtract_usage(left, right)

results in

UsageMetadata(
    input_tokens=2,
    output_tokens=2,
    total_tokens=4,
    input_token_details=InputTokenDetails(cache_read=4),
    output_token_details=OutputTokenDetails(reasoning=0),
)

Parameters:

left (UsageMetadata | None) – The first UsageMetadata object.
right (UsageMetadata | None) – The second UsageMetadata object.

Returns:

The resulting UsageMetadata after subtraction.

Return type:

UsageMetadata